Natural Resources Group

Paper 96-02

CIMMYTSustainable Maize

and Wheat Systems

for the Poor

Soil Fertility Management

Research for the Maize Cropping

Systems of Smallholders in

Southern Africa: A Review

John D.T. Kumwenda,

Stephen R. Waddington,

Sieglinde S. Snapp,

Richard B. Jones,

and Malcolm J. Blackie

37

Natural Resources Group

Paper 96-02

Soil Fertility Management Research

for the Maize Cropping Systems of

Smallholders in Southern Africa:

A Review

John D.T. Kumwenda, Stephen R. Waddington, Sieglinde S. Snapp,Richard B. Jones, and Malcolm J. Blackie *

CIMMYT

* John D.T. Kumwenda is Senior Agronomist with the Maize Commodity Team, Ministry of Agriculture and LivestockDevelopment, Malawi. Stephen R. Waddington is an Agronomist with the CIMMYT Maize Program and is based inZimbabwe. Sieglinde S. Snapp is a Postdoctoral Fellow of the Rockefeller Foundation, posted to the Southern AfricaAgricultural Sciences Program, Malawi. Richard B. Jones is with the Agroforestry Commodity Team/WashingtonState University, based in the Ministry of Agriculture and Livestock Development, Malawi. Malcolm J. Blackie is aSenior Scientist with the Rockefeller Foundation and is with the Southern Africa Agricultural Sciences Program,Malawi. The views expressed in this paper are the authors’ and may not necessarily reflect CIMMYT policy. Aversion of this paper will appear in The Emerging Maize Revolution in Africa: The Role of Technology, Institutions, andPolicy (C.K. Eicher and D. Byerlee, eds., forthcoming).

CIMMYT is an internationally funded, nonprofit scientific research and training organization.Headquartered in Mexico, the Center is engaged in a research program for maize, wheat, and triticale,with emphasis on improving the productivity of agricultural resources in developing countries. It isone of several nonprofit international agricultural research and training centers supported by theConsultative Group on International Agricultural Research (CGIAR), which is sponsored by the Foodand Agriculture Organization (FAO) of the United Nations, the International Bank for Reconstructionand Development (World Bank), and the United Nations Development Programme (UNDP). TheCGIAR consists of some 40 donor countries, international and regional organizations, and privatefoundations.

CIMMYT receives core support through the CGIAR from a number of sources, including theinternational aid agencies of Australia, Austria, Belgium, Brazil, Canada, China, Denmark, Finland,France, India, Germany, Italy, Japan, Mexico, the Netherlands, Norway, the Philippines, Spain,Switzerland, the United Kingdom, and the USA, and from the European Union, Ford Foundation,Inter-American Development Bank, OPEC Fund for International Development, UNDP, and WorldBank. CIMMYT also receives non-CGIAR extra-core support from the International DevelopmentResearch Centre (IDRC) of Canada, the Rockefeller Foundation, and many of the core donors listedabove.

Responsibility for this publication rests solely with CIMMYT.

Printed in Mexico.

Correct citation: Kumwenda, J.D.T., S.R. Waddington, S.S. Snapp, R.B. Jones, and M.J. Blackie. 1996.Soil Fertility Management Research for the Maize Cropping Systems of Smallholders in Southern Africa: AReview. NRG Paper 96-02. Mexico, D.F.: CIMMYT.

Abstract: This paper examines the implications of declining soil fertility for the maize-based croppingsystems in southern and eastern Africa. A review of the importance of maize in the region is followedby a description of the economic and agronomic circumstances of smallholders who produce maize.Next, the paper examines technologies currently available for enhancing soil fertility, includingtechnologies for increasing inorganic/organic fertilizer use and fertilizer-use efficiency and thedevelopment of maize genotypes that perform well despite low soil fertility. Ways of facilitatingfarmers’ adoption of better soil fertility management practices are described, based on examples drawnfrom recent research, particularly in southern Africa. A new model for soil fertility research andextension is proposed. The model features the use of organic as well as inorganic sources of nutrientsand actively involves farmers and others in an integrated, long-term process for improving soil fertilityin southern and eastern Africa.

Additional information on CIMMYT activities is available on the World Wide Web at:http://www.cimmyt.mx or http://www.cgiar.org

ISSN: 1405-2830AGROVOC descriptors: Zea mays; soil management; soil fertility; soil exhaustion; cropping systems;fertilizer application; innovation adoption; economic environment; research projects; small farms;Southern Africa; East AfricaAGRIS category codes: P35, E14Dewey decimal classification: 631.45

Contents

Page

iv Tablesiv Figuresiv Acknowledgmentsv Executive Summary

1 Introduction

1 The Importance and Characteristics of Smallholder Maize Systems

2 Overview of Soil Fertility Constraints to Maize Production3 Low use of inorganic fertilizer4 Declines in soil organic matter5 Insufficient attention to crop nutrition studies

6 Improved Soil Fertility and Productivity: Practicable Options for Farmers7 Smallholder diversity, cash and labor constraints, and soil fertility management8 Increasing fertilizer use and fertilizer-use efficiency

10 Increasing the availability and use of organic sources of fertility15 Improving maize genotypes for soils with low fertility15 The way forward

16 Linking Adaptive and Process Research to ImproveTechnology Development and Dissemination

17 A case study in applied research: Overcoming micronutrientdeficiencies for maize in Malawi

19 Basic process research

23 Exploiting Interactions of Soil Fertility Technologies withOther Inputs and Management Factors

23 Interactions with weed management24 Interactions with moisture

25 Institutional Change in Research and Development Organizations25 Addressing smallholder diversity27 Institutional change to support smallholder productivity increases

29 References

iv

Tables

Page

10 Table 1. Examples of gains in maize yield obtained through combinations of organic andinorganic fertilizer at levels practicable on farmers’ fields, Malawi and Zimbabwe

17 Table 2. The relief of micronutrient deficiencies on maize in Malawi: an example of a long-term research process

Figures

6 Figure 1. Maize production scenarios for 1995-2015, Malawi

21 Figure 2. The role of high-quality organic inputs in improving the efficiency of inorganicfertilizer use

23 Figure 3. Effect of weeding frequency and N application on maize grain yield

Acknowledgments

We thank Paul Heisey, Greg Edmeades, Derek Byerlee, and Carl Eicher for many helpfulsuggestions on drafts of this review. We also thank the design staff at CIMMYT in Mexico, headedby Miguel Mellado, for help with layout and publishing, and we appreciate Tim McBride’sassistance in helping with final corrections of galleys and distribution of the publication.

v

Executive Summary

The dominant smallholder cropping systems of southern Africa are based on maize. Increasinghuman population density and declining land availability have made shifting cultivation obsolete,and maize is now continuously cropped in many areas. The fallows which traditionally restoredsoil fertility and reduced the buildup of pests and diseases are disappearing from the agriculturallandscape. The soil resource is being degraded, with a consequent reduction in crop yield.

Despite the notable adoption of high-yielding maize by smallholders in Africa (improvedgermplasm is grown on 33-50% of Africa’s maize area), national per-hectare increases in maizeproductivity are disappointing. Losses of mineral nutrients from soil generally exceed nutrientinputs. Presently the challenge of improving productivity without compromising sustainability isso large that farmers will need to combine gains from improved germplasm with complementaryimprovements in their management of soil fertility. Improved germplasm alone will not besufficient to meet the challenge. Both research and extension organizations must place far greateremphasis on the complex issues related to building up and maintaining soil fertility under theincome and other constraints faced by smallholders.

Inorganic fertilizers are expensive and not very profitable for smallholders to use, especiallybecause impractical blanket applications of fertilizer are recommended even in semiarid areas. Theprofitability of using fertilizer must be increased for farmers who can afford fertilizer. This urgenttask can be accomplished by developing improved fertilizer management techniques that areappropriate for smallholders and by ensuring that recommendations are better targeted tosmallholders’ circumstances.

Fertilizer-use efficiency is often low because of the declining level of organic matter in tropicalsoils. For this reason, the proportion of locally produced organic materials must be increased tomaintain soil organic matter and halt the downward spiral of soil fertility. Improving theefficiency of inorganic fertilizer use in various ways, including the addition of soil micronutrientsand small amounts of high-quality organic matter, will consolidate and expand the base offertilizer users.

In many households, the cash required to buy inorganic fertilizer far exceeds total annual cashincome. The lack of cash dominates decision making at the household level and is central to thedevelopment of adoptable technologies. Many farm households are forced to sell their labor inreturn for food or cash, which, in turn, compromises their own agricultural efforts. For thisexpanding group of farmers, the best strategy for increased soil fertility is to give more emphasisto organic sources of nutrients, especially legumes, that capitalize on the freely available nitrogenin the atmosphere.

vi

Legumes are not new to farming systems. Grain legumes, legume intercropping and rotations,green manures, improved fallows, agroforestry, cereal residues, and animal manures can allenhance soil fertility and sustain the resource base. However, in broad terms, the larger the soilfertility benefit from a legume technology is likely to be, the larger the initial investment requiredin labor and land, and the fewer short-term food benefits it has. The potential of such technologiesis rarely realized on farmers’ fields.

Although combinations of low rates of several inputs show promise, especially combinations ofinorganic and organic fertilizer, such combinations still have a cash cost. Innovative mechanismsare needed to help farmers begin to access such inputs. One promising approach involvesproviding farmers with start-up grants of cash paid into savings schemes, from which farmers canobtain loans.

Basic, process-based research provides the foundation for extrapolating from site-specific trials toagronomic recommendations for specific agroecological zones and farmer groups. Past crophusbandry research is often neglected because the results are distilled into a fewrecommendations that ignore the important interactions in the system and fail to address thewidespread diversity that exists among smallholders. Institutional memory not only needs to bemaintained but must be expanded to a wider group, in part through computer databases andeffective networks. The emphasis in both research and extension needs to move away from a rigidand prescriptive approach to a flexible problem-solving format leading to conditionalrecommendations. This will facilitate the evolution of a technology development process drivenby smallholders’ needs. Failure to develop such a process will result in a weakening naturalresource base and a continuing decline in the standard of living of rural communities reliant onagriculture in southern Africa.

1

Soil Fertility Management Research for the Maize CroppingSystems of Smallholders in Southern Africa:

A Review

John D.T. Kumwenda, Stephen R. Waddington, Sieglinde S. Snapp,Richard B. Jones, and Malcolm J. Blackie

Introduction

It is increasingly evident that declining soilfertility is the most widespread, dominantlimitation on yields of maize (Zea mays L.) andon the sustainability of maize-based croppingsystems in southern and eastern Africa.Technologies that smallholders can use tosustain soil fertility are still relatively scarce. Ifresearchers and farmers do not make a morevigorous attempt to address the extensivedecline in soil fertility, the productivity ofmaize-based farming systems will fail toincrease, and improved maize germplasm willhave only a transitory effect on productivity insmallholders’ fields.

In this paper, we explore strategies for buildingup and maintaining soil fertility in southern andeastern Africa despite the income constraints —and, increasingly, land and labor constraints —facing smallholders. We draw heavily onexamples from southern Africa, particularlyMalawi and Zimbabwe, for three reasons. First,our experience there is considerable. Second,Malawi and Zimbabwe offer contrastingportraits of an agriculture in crisis, increasinglyunable to meet national food needs (Malawi),and one of the most successful agriculturalbases in sub-Saharan Africa (Zimbabwe). Third,the experience with soil fertility constraints insouthern Africa is relevant to many other areasof sub-Saharan Africa.

We begin with an overview of maize insouthern and eastern Africa: its importance for

food security, the conditions under whichsmall-scale farmers grow the crop, and theevidence that even as more farmers turn toimproved maize for higher yields, these effortsare frustrated by a persistent decline in soilfertility that reduces productivity. Next, welook at technologies currently available forenhancing soil fertility and proceed to outline,based on examples drawn from practice, waysof facilitating farmers’ adoption of better soilfertility management practices. We thenpropose a model for soil fertility research andextension that features the use of organic aswell as inorganic alternatives and activelyinvolves farmers and others in an integrated,long-term process for improving soil fertility insouthern and eastern Africa.

The Importance and Characteristicsof Smallholder Maize Systems

The dominant smallholder cropping systems ofsouthern and eastern Africa are based onmaize, the staple food, which accounts forabout 50% of the calories consumed. Foodsecurity in resource-poor households iscritically linked to the productivity andsustainability of maize-based croppingsystems, which are found from sea level (thecoastal zones of Mozambique and Tanzania) toelevations above 2,400 m, and from dry areasreceiving less than 400 mm of rainfall (southernZimbabwe, southern Mozambique) to well-watered areas (the higher equatorial zones).Maize accounts for 60% or more of the croppedarea in Malawi, Zimbabwe, and Zambia and is

2

almost as important in Mozambique, Tanzania,and Kenya. In Malawi, where populationdensity in the southern region reaches anaverage of 215 persons per square kilometer,maize is the main crop on nearly 90% ofcultivated area and contributes 80% of the dailyfood calories. The growing popularity of maizein Malawi has been attributed to its efficiency asa per-hectare calorie producer compared toother food plants (Carr 1994). As crop landbecomes more scarce, the efficiency of calorieproduction per hectare assumes greaterimportance for farmers.

Most farm households rely on family resources,especially labor, to grow maize on 0.5-3.0 ha ofland held under traditional tenurearrangements. Human labor — aided by hand-held hoes — is the predominant means of maizeproduction across Malawi, northern and easternZambia, northern Mozambique, and many partsof Tanzania (Low and Waddington 1990,Waddington 1994). Elsewhere in the region,particularly southern Zambia, Botswana, andZimbabwe, animal (mainly ox) traction is usedto prepare land and help with weeding. Somefarmers still grow maize in loose rotations withsuch crops as groundnuts and sunflowers, butincreasingly maize is planted on the same landyear after year, often sparsely intercropped withbeans, groundnuts, cowpeas, or pumpkins.Formal intercropping is common only wherehuman population density is high and averageland holdings per family small, as in parts ofsouthern Malawi, where each farm householdhas access to only about 0.8 ha.

Traditionally, African agricultural systems werelargely based on extended fallows and theharvesting of nutrients stored in woody plants.The site to be cultivated was cleared by cuttingand slashing plant growth and burning thedried plant material (e.g., Araki 1993, Blackieand Jones 1993, Blackie 1994). Extensive

exploitation of land by a few familiescharacterized these systems: for example, in thechitemene slash-and-burn system in the miombowoodland of northern Zambia, land wasfallowed for 50-70 years, followed by croppingin the center of the clearing for a few years(Araki 1993). Today in most arable areas ofMalawi, Zimbabwe, and Kenya, fallowing hasalmost disappeared from the agriculturalsystem. The length of the fallow continues todecline significantly in Zambia, Mozambique,and Tanzania. Continuous maize cropping andthe resulting downward spiral of soil fertilityhave reduced crop yields and exacerbated soilerosion (Araki 1993). In some areas, such as thewetter communal lands of northern Zimbabwe,soil is so severely depleted that withoutfertilizer maize will yield virtually no grain.

In many parts of Africa, including southernAfrica, farmers have switched from traditionalmaize landraces to improved germplasm in thelast 25 years. Byerlee et al. (1994) calculatedthat improved varieties and hybrids covered33-50% of the maize area in Africa, but there islittle evidence of greater maize productivity perhectare (CIMMYT 1992, 1994; Lele 1992).Productivity increases are disappointing evenin countries where smallholders now usesubstantially more fertilizer (Conroy 1993). Allof these circumstances emphasize the urgentneed for further research on strategies forovercoming soil fertility problems. In the nextsection of this paper, we turn our attention to amore detailed description of the types andextent of Africa’s soil fertility problems.

Overview of Soil FertilityConstraints to Maize Production

Average maize yields per unit of land havefallen in Africa partly because maize croppinghas expanded into drought-prone, semiaridareas (see, for example, Gilbert et al. 1993), but

3

cultivated with annual crops in the uplandtropics are very prone to erosion) will reducethese yield levels considerably. Becausefarmers are locked into low crop productivityper unit of land from a degrading naturalresource base, they will increasingly be forcedto encroach on ecologically fragileenvironments such as the Zambezi andLuangwa Valleys, with their uniqueecosystems and remnant habitats for severalendangered large mammals, and on the manyhilly areas where loss of protective vegetationwill quickly lead to severe erosion.

These bleak circumstances are exacerbated bythree limitations to change that are endemic insub-Saharan Africa: the low use of inorganicfertilizer, declining soil organic matter, andinsufficient attention to crop nutrient studies.

Low use of inorganic fertilizerIn most parts of the world, chemical fertilizersplay a major role in maintaining or increasingsoil fertility, but farmers in sub-Saharan Africause very little chemical fertilizer. The FAO(1988) has estimated that the average fertilizerapplication in sub-Saharan Africa is 7 kg offertilizer nutrients per hectare of arable landplus permanent crops per year. More recentcalculations for 1993 by Heisey and Mwangi(1995), using similar criteria, give an average of10 kg of fertilizer nutrients per hectare.Chemical fertilizer use is higher in somecountries of southern Africa (notablyZimbabwe, Zambia, and Malawi) where thecommercial farming sector is relatively welldeveloped and fertilizer-responsive maize animportant crop. Fertilizer application rates onmaize have been calculated at 70 kg fertilizernutrients per hectare of maize crop per year inZambia, 55 kg in Zimbabwe, and 26 kg inMalawi (Heisey and Mwangi 1995).Nevertheless, these levels are well below cropand soil maintenance requirements and are

a much greater negative influence on maizeyield has been the loss of soil fertility,especially in wetter areas where yield potentialis higher.

The old and already highly leached soils inAfrica’s humid and sub-humid zones haveinherently low nutrient levels. Sandy andsandy loam soils derived from granite, withorganic matter of less than 0.5% and very lowcation exchange capacities, are widespread inZimbabwe, southern Zambia, and western andsouthern Mozambique. Nitrogen deficiency isubiquitous on these soils, while deficiencies ofphosphorus (P), sulfur (S), magnesium (Mg),and zinc (Zn) are common (Grant 1981). On thesandy loam and clay loam soils in Malawi,which are chronically deficient inmacronutrients, micronutrients such as S, Zn,and boron (B) are reported to be limiting atmany sites (Wendt, Jones, and Itimu 1994).Zambia and Mozambique have large areas ofacidic soils with free aluminum (Al3+).

The largest aggregate nutrient losses in Africaare seen in major maize-producing countrieswith higher population densities and erosionproblems. Smaling (1993) and Stoorvogel,Smaling, and Janssen (1993) estimated thatannual net nutrient depletion exceeded 30 kgnitrogen (N) and 20 kg potassium (K) perhectare of arable land in Ethiopia, Kenya,Malawi, Nigeria, Rwanda, and Zimbabwe.

Buddenhagen (1992) estimated that,discounting the effects of erosion, theweathering of minerals and biological Nfixation will enable, at most, 1,000 kg/ha ofmaize grain to be produced each year on asustainable basis in the tropics. In hot lowlandareas, such as Ghana, this equilibrium isestimated to be even lower, at 600-800 kg/ha ofmaize grain annually (G. Edmeades, pers.comm.). Soil loss through erosion (and soils

4

likely to remain so, because fertilizer isprobably the most costly cash input used bysmallholders in southern Africa.

Aside from its cost, fertilizer is not used morewidely because fertilizer recommendations arefrequently unattractive to smallholders.Recommendations often ignore soil andclimatic variation in the areas farmed bysmallholders, are incompatible withsmallholders’ resources, or are simplyinefficient. All of these shortcomings leadfarmers who do apply fertilizer to incurunnecessary expense. For example, inZimbabwe farmers are instructed to applybasal fertilizer for maize in the planting hole atplanting, but instead farmers almost alwaysapply fertilizer just after crop emergence,which is easier, less risky, and results in anegligible loss of yield under farm conditions(Shumba 1989). This practice allows farmers,after a given rain, to plant more area morequickly (important on a drying sandy soil), getbetter crop emergence, and make more laboravailable for other operations. Anotherexample of an inappropriate recommendationhas to do with the type of fertilizerrecommended. There is rarely a response to Kon the granite soils predominant insmallholder farming areas of Zimbabwe(Mashiringwani 1983, Hikwa andMukurumbira 1995), yet the recommendedcompound fertilizer contains K as well as Nand P. A better option might be to applycheaper N alone, just after planting, andcheaper forms of P at other times.

Even when fertilizer is used, the efficiency ofits use on farmers’ fields (measured by thegrain yield response to the addition ofchemical N and P fertilizers) is often poor,which reduces the profitability of fertilizer use.Jones and Wendt (1995), summarizing datafrom farmers’ fields in Malawi and Zambia,

calculated that farmers using current fertilizerpractices can expect just 9.5-16 kg of maizegrain per kilogram of nutrient applied to localunimproved maize and 17-19 kg of maize grainper kilogram of nutrient applied to hybrids.Research on farms in Malawi shows that, atfarmers’ levels of fertilizer application,improved timing and application methods canraise the response of unimproved maize tonitrogen from 15 to 20 kg grain per kilogram ofN applied and raise the response of hybridmaize from 17.4 to 25 kg grain. Furthermore,this improvement in fertilizer-use efficiencywould substantially outweigh any feasiblechanges in fertilizer or maize prices in makingfertilizer more attractive to smallholders (HIID1994). One example of the limited profitabilityof inorganic fertilizer has been reported byConroy and Kumwenda (1995); they notevalue:cost ratios in Malawi of 1.8 for fertilizeron hybrid maize and 1.3 on unimproved maizefor moving from zero fertilizer to currentrecommended levels.

Declines in soil organic matterIn the tropics, the maintenance andmanagement of soil organic matter (SOM) arecentral to sustaining soil fertility onsmallholder farms (Swift and Woomer 1993,Woomer et al. 1994). In low-input agriculturalsystems in the tropics, SOM helps retainmineral nutrients (N, S, micronutrients) in thesoil and make them available to plants in smallamounts over many years as SOM ismineralized. In addition, SOM increases soilflora and fauna (associated with soilaggregation, improved infiltration of water andreduced soil erosion), complexes toxic Al andmanganese (Mn) ions (leading to betterrooting), increases the buffering capacity onlow-activity clay soils, and increases water-holding capacity (Woomer et al. 1994). CurrentSOM inputs are insufficient to maintain organicmatter levels in tropical agricultural soils.

5

Continuous cropping, with its associated tillagepractices, provokes an initial rapid decline inSOM, which then stabilizes at a low level (forexample, see Woomer et al. 1994).

The conventional mechanisms for addressinglosses of SOM in tropical, rainfed, low-inputsystems are fallowing, rotations (especiallyinvolving legumes), the addition of animalmanures, forms of intercropping (includingintercropping with hedgerow legumes), andreduced tillage.1 In southern Africa,agricultural intensification is often associatedwith the diminished availability of animalmanures. As pressure on arable land rises,cropping encroaches on areas previously usedfor grazing, and livestock production becomesmore difficult. This problem is more commonin the unimodal rainfall areas of southernAfrica, where the long dry season makes zero-grazing techniques difficult or impossible forsmallholders, than in the bimodal rainfall areasof eastern Africa. Manure from cattle and otheranimals is very important for most farmers inZimbabwe, less so in Zambia, but rarelyavailable in Malawi (where animals are scarce).But even in the best areas, the supply (and, asimportant, the quality) of animal manure isinadequate to maintain soil fertility on its own.

Where animals are few, farmers have turned toother sources of SOM. Leaf litter from trees canmake significant contributions in areas close towoodlands, but as population grows, thedeforestation associated with the demand forarable land, building material, and fuel worksagainst this option. Although composted cropresidues are used in wetter areas and wherecrop biomass production is relatively high,composts are rarely sufficient for more than amodest part of the cultivated area, and, like

manures, their quality is often poor. Thesetechnologies require substantial labor fromfarmers (for examples from Zimbabwe, seeHuchu and Sithole, 1994, and Carter 1993). Thereality is that organic matter is rarely sufficientto maintain SOM, and in marginal areas whererainfall is low it is impossible to grow enoughbiomass to maintain SOM. Furthermore, theproductivity boost that smallholders needcannot be supplied by organic manures alone.The use of manures will need to be combinedwith the judicious use of chemical fertilizers,improved pest and weed managementtechniques, and the use of high-yielding cropvarieties.

Insufficient attention tocrop nutrition studiesIn Africa, the research agenda has been biasedaway from crop nutrition studies and towardsthe gains that may be obtained through plantbreeding. This bias is a legacy of the GreenRevolution in Asia, which succeeded throughthe use of improved germplasm under verydifferent conditions — particularly Asia’s morefertile and uniform soils — than thoseprevailing in Africa. Improved maize materialscan make better use of available nutrients, butin the absence of added nutrients, the gainsfrom genetic improvement alone are small.Under low N conditions, maize scavenges theN available in the soil very effectively, andlittle N is left for the plant to take up byflowering (G. Edmeades, pers. comm.). Forexample, results from an extensive program ofon-farm demonstrations over four seasons inthe major maize-growing areas of Malawishowed that on relatively fertile soils andunder good management, hybrids withoutfertilizer yielded just 1.4 t/ha compared with0.9 t/ha for unimproved maize (Jones and

1 Some of these techniques are used in temperate agriculture, but farmers in temperate areas still rely more heavily onpurchased inputs.

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Wendt 1995; Conroy and Kumwenda 1995;Zambezi, Kumwenda, and Jones 1993). InAfrica, the challenge of increasing productivitywithout compromising sustainability is so largethat farmers will need to combine gains fromimproved germplasm with complementaryimprovements in their management of soilfertility. The central issue is how to build upand maintain soil fertility under the incomeand, increasingly, land and labor constraintsfaced by smallholders.

Essentially two approaches can be used inmanaging soil fertility (Sanchez 1995). The bestknown approach, used in producing most ofthe world’s food, involves overcoming soilconstraints to meeting plant requirementsthrough the application of purchased inputs. Infact, much of the increase in crop yields indeveloping countries since the GreenRevolution, especially in Latin America andAsia, can be attributed to the purchased inputsused by greater numbers of farmers (Pinstrup-Andersen 1994). The second approach reliesmore on biological processes to optimizenutrient cycling, minimize the use of externalinputs, and maximize theefficiency of input use. Ourunderstanding of theprinciples underlying thissecond, more complexapproach is not welldeveloped, and knowledgegained in temperate areasmay be inappropriate forsmallholder agriculture inthe tropics. These twoapproaches, and a moresustainable, practicablemiddle way that combinesthe best features of both, will

be discussed throughout this paper as weexamine practicable alternatives forsmallholders.

Improved Soil Fertilityand Productivity:

Practicable Options for Farmers

The strong contribution of better managementpractices to sustaining and increasingproductivity is highlighted in Figure 1. Figure1 presents three scenarios, based on “best bet”estimates of technology adoption for Malawi,in which a maize deficit or surplus iscalculated based upon the balance betweenmaize production and consumption in a givenyear. Assumptions include a populationgrowth rate of 3.2% per year; per capita annualmaize consumption of 230 kg; and a constantmaize area of 1.4 million hectares,2 20% ofwhich is planted to improved maize at thestart of each scenario. Calculations are basedon national average yields of hybrid andunimproved maize for 1982-92 (these datainclude fertilized and unfertilized fields)(Ministry of Agriculture Crop Estimates,

20181614121086420

Scenario 2: Hybrid maize Scenario 3: Same asarea increases 2 + better management

Figure 1. Malawi maize production scenarios for 1995-2015.

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Scenario 1: Current maize and management

2 Virtually all of the arable land available to smallholders in Malawi is under continuous maize cultivation, so theopportunities for an expansion of maize area are limited.

7

quoted by Conroy 1993). In all scenarios, theyield of unimproved maize is 1,000 kg/ha.

Under scenario one, the yield of improvedmaize is held constant at 2,500 kg/ha and thearea planted to improved maize does notchange. This scenario represents a continuationof the status quo in Malawi, where a wideningdeficit between national maize production andconsumption is already apparent. Underscenario two, the adoption of hybrid maizeincreases by 20% (compounded) each year, buthybrid yields remain at 2,500 kg/ha becausethere is little change in soil fertility or othermanagement practices. Under this scenario,maize production shows a modest surplus by2002 but lapses back into a deficit just six yearslater. Finally, under scenario three the adoptionof hybrid maize (as in scenario two) is combinedwith the gains in efficiency achieved from betterfertilizer management by farmers of about 44%3

and with other likely managementimprovements, particularly timely weeding(Kabambe and Kumwenda 1995). A yieldincrease of 68% is assumed when farmers usethis set of improved management practices withtheir hybrid maize. Under this scenario largesurpluses are achieved to 2015. Projecteddeclines in the rate of human populationgrowth make it likely that grain surpluses couldbe maintained even beyond 2015. Productivityimprovements would thus make a differencewell into the 21st century.

Although there is little argument about the needfor more sustainable soil fertility management,there is less clarity on how it might be achieved.In a major overview of past impacts and futureprospects for maize research in sub-SaharanAfrica, Byerlee et al. (1994) contrasted farmers’high level of adoption of improved maizeagainst the relative lack of technology for

maintaining soil fertility and increasing laborproductivity. Many resource managementtechnologies are potentially available, but feware actually easy for farmers to adopt. Tounderstand why this is so, we must look moreclosely at the circumstances under whichincreasing numbers of smallholders in Africaoperate. Then we will review technologies forenhancing soil fertility to suggest how theymight be made more attractive to farmers. Wethen proceed to outline, based on examplesfrom practice, improvements in technologydevelopment and transfer that would facilitatesmallholders’ adoption of better soil fertilitymanagement practices.

Smallholder diversity, cash and laborconstraints, and soil fertility managementThe smallholder farm sector is characterized byconsiderable variability in individual access toland (in quality and quantity), resources, andskills. Literacy and numeracy are poor. Thepopulation involved in agriculture ranges fromsmall-scale commercial farmers, throughprogressive farmers, to the vast majority ofpoorer people who endeavor to subsist, withvarying levels of success, in hostile ecologieswhere the sustainability of life, livelihood, andenvironment is threatened.

The lack of cash is a dominant influence on thechoices farmers make. The two major costsfaced by smallholders in producing maize arelabor and fertilizer. Labor may be provided bythe family, it may be bought in from otherfarmers, and it may be sold to others for foodor cash. Often the farm household is headed bya woman, who has small children. Olderchildren may be at school or may have movedto town. If the woman is fortunate, herhusband and the children who live away fromhome will still help support the rural

3 See the earlier section of this paper, “Low use of inorganic fertilizer.”

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household through cash or kind. If they do not,she must attempt to support herself and herchildren from what she can grow or sell. Shewill be living on a piece of land that has beencultivated many times before, whose inherentfertility has long been exhausted. Weeds willhave established themselves and will competestrongly for light, water, and nutrients withwhatever she plants.

Given a hectare or more of land, the womanmay be self-sufficient in food if her health isgood and the weather favorable. But at the startof the rains people often suffer from malariaand diarrhea, and illness of the farmer or herchildren will delay planting. If the rainy seasonis poor (and “Africa” and “drought” havebecome nearly synonymous to many), her cropmay fail. The odds are that in some years, oftenin many, she will not produce enough food forher family’s needs. This failure will require herto work for neighboring farmers who will thenfeed or pay her (and any children who workwith her) for labor. While she plants, weeds, orfertilizes the neighbor’s crop, her own is leftunplanted, unweeded, and unfertilized untillater in the season. Late planting and poorweeding lead to a poor harvest, and once againthe farmer will find herself without food beforethe next crop comes in.

This is the cycle that the next maize revolutionhas to break. Increasing numbers of ruralfamilies in Africa cannot produce sufficientfood for their annual needs (Weber et al. 1988).Malawi offers a view of what the future couldlook like for many more Africans unless currenttrends are reversed: in Malawi some 60% ofrural households (41% of the total population)produce less than they require to feedthemselves through the year. The amount ofcash such a household needs to buy inorganicfertilizer far exceeds its total annual cashincome (HIID 1994).

Clearly, African smallholders, almostwherever they live, face conditions ofdifficulty and stress for which both traditionand science have few real answers. Althoughtechnically sound solutions to many of theirproblems exist, all too often these solutionsturn out to be financially or manageriallyunsound. Nevertheless, some solutions mayprove feasible for smallholders.

Increasing fertilizer use andfertilizer-use efficiencyIncreasing the number of smallholders usingfertilizers — Since the 1960s, fertilizer use hasbeen growing in sub-Saharan Africa at around6.7% annually (Heisey and Mwangi 1995), butmany farmers still do not use fertilizers, whichwill remain a high-cost item for theforeseeable future. The base of fertilizer userscannot be consolidated and expanded withoutgenerating better returns from fertilizerthrough increased efficiencies in its use. Muchgreater use will also need to be made oforganic sources of fertility to improve fertilitymanagement and reduce cost. How cancurrent fertilizer users, and those who arelikely to be able to afford some fertilizer,achieve increases in fertilizer-use efficiency? Athree-pronged strategy is envisaged, in which:

• the type of inorganic fertilizer and its useare carefully tailored to the conditions facedby smallholders;

• the proportion of locally produced organicmaterials is increased, which will not onlyreduce the cash cost of fertilizer but increasethe efficiency of inorganic fertilizer use; and

• agronomic and economic factors receivegreater consideration when breedingpriorities are established for maize andlegumes, so future improved materials fitsmallholders’ circumstances.

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Increasing inorganic fertilizer-use efficiency— A central part of any strategy for expandingthe number of smallholders who use inorganicfertilizer will be to determine how to make thebest use of the limited amounts of fertilizer thata typical smallholder is able to purchase.Increasing fertilizer-use efficiency will require asignificant shift in thinking for both researchersand policy makers in Africa. For instance,Zimbabwe has a fifty-year history ofagricultural research on inorganic fertilizers,but much of this work was geared towardsusers who could afford relatively largequantities of fertilizer (the large commercialfarms and growers of cash crops). SinceIndependence in 1980, a great deal of work hasexamined the appropriateness of types,amounts, timing, and placement of inorganicfertilizers for food crops produced bysmallholders,4 yet recommendations forinorganic fertilizer have not given sufficientattention to the cash constraints and the riskfaced by resource-poor farmers in marginalareas. Of the 32% of farmers in Zimbabwe whofollowed the fertilizer recommendations fortheir maize crop in the near-average season of1990/91, 48% failed to recover the value of thefertilizer (Page and Chonyera 1994).

Additions of soil micronutrients can improvethe yield response to macronutrients (N and P)on deficient soils. Nutrients such as Zn, B, S,and Mg can often be included relativelycheaply in existing fertilizer blends; whentargeted to deficient soils, these nutrients candramatically improve fertilizer-use efficiencyand crop profitability. During the 1950s, 1960s,and 1970s, S, Mg, and (less commonly) Zn andB deficiencies were detected for maize on sandysoils in Zimbabwe (Grant 1981, Metelerkamp1988). Enhanced yields were obtained by

including selected micronutrients in fertilizerblends (Grant 1981). Recent experience in Malawiprovides a striking example of how N fertilizerefficiency for maize can be raised by providingappropriate micronutrients on a location-specificbasis. Supplementation by S, Zn, B, and Kincreased maize yields by 40% over the standardN-P recommendation alone (Wendt, Jones, andItimu 1994).5

There is evidence that the most promising route toimproving inorganic fertilizer efficiency insmallholder cropping systems is by adding smallamounts of high-quality organic matter to tropicalsoils (Ladd and Amato 1985; Snapp 1995). High-quality organic manures (possessing a narrow C/N ratio and a low percentage of lignin) providereadily available N, energy (carbon), andnutrients to the soil ecosystem, and they build soilfertility and structure over the long term. Theiruse will increase soil microbial activity andnutrient cycling and reduce nutrient loss fromleaching and denitrification (De Ruiter et al. 1993;Doran et al. 1987; Granastein et al. 1987; Snapp1995).

Two long-term cropping studies in Kenya andNigeria indicate that organic plus inorganicinputs sustain fertility at a higher level than theexpected additive effects of either input by itself(Dennison 1961). Nutrient effects alone do notexplain the benefits derived from modestamounts of organic manure combined withinorganic fertilizers. High-quality carbon andnitrogen provide substrate to support an activesoil microbial community. Soil microbes arevaluable not so much because they supplynutrients directly, but because they enhance thesynchrony of plant nutrient demand with soilsupply by reducing large pools of free nutrients(and consequent nutrient losses from the system).

4 See Grant (1981), Metelerkamp (1988), and a recent summary by Hikwa and Mukurumbira (1995).5 For details, see “A case study in applied research,” later in this paper.

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Thus microbes maintain a buffered, activelycycled nutrient supply (De Ruiter et al. 1993;Snapp 1995). Research is now generatingexamples of yield gains available on farmers’fields in southern Africa through inorganic/organic combinations (Table 1 gives threerecent examples). Often the largest gains areseen on research stations where soil fertility isalready high. On-farm gains are usually lowerbecause of inherently low soil fertility, waterdeficits, and management compromises, butthis practice is still worthwhile. Many farmersalready recognize these effects and combine,where possible, small amounts of high-qualityorganic inputs with inorganic nutrients.

Increasing the availability and use oforganic sources of fertilityAs noted earlier, the organic inputs available tomost smallholders are rarely sufficient tomaintain SOM, and more organic materialsmust be introduced rapidly into smallholders’cropping systems. Options include rotations,green manures, animal manures, intercropping,strip cropping, relay cropping, and agroforestry.

The role of legumes — Most of the promisingroutes to increased SOM involve legumes,which have been the focus of well-meaningefforts to transform smallholder Africanagriculture since the turn of the century.

Table 1. Examples of gains in maize yield obtained through combinations of organic andinorganic fertilizer at levels practicable on farmers’ fields, Malawi and Zimbabwe

Maize grain yield (t/ha) Yield ofcombination as

Organic + a percentageOrganic Inorganic Location No Organic Inorganic inorganic of alonefertilizer fertilizer and season fertilizer alone alone combination treatments

Leucaena 30 kg N/ha Chitedze 2.24 3.32 2.72 3.60 119leucocephala applied to Researchalley cropped maize crop Station,with maize; Malawi,1.5-2.5 t/ha 1988-90Leucaenapruningsapplied tomaize

Pigeonpea 48 kg N/ha Luyangwa 0.87 1.70 1.98 2.31 126intercopped applied to Researchwith maize maize crop Station,in previous Malawi,season; 1993-95pigeonpearesiduesincorporatedinto the soil

Cattle manure: 112 kg N, 6 communal 0.79 1.11 1.30 1.93 16013-25 t/ha 17 kg P, and farms, Wedzabroadcast 16 kg K/ha and Chinyika,and plowed as split basal Zimbabwe,in before and topdress 1994/95 seasonplanting applications (a drought year)

Note: These gains are from the first cropping season after fertilizer application. Additional gains can be expectedin following seasons.

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The efforts of Alvord in Zimbabwe are typicalof the genre. Green manures were heavilyresearched from the 1920s to 1940s(Metelerkamp 1988), and large-scalecommercial farmers used green manureswidely until the real price of inorganicfertilizers fell in the 1950s and green manuringbecame uneconomic. However, rising realprices of inorganic fertilizers and concern overthe sustainability of current cropping systemshave once again attracted interest in greenmanures (see Hikwa and Mukurumbira 1995).

Annual legumes are used as sole crops inrotation with cereals, are intercropped, or areoccasionally used as green manures. Perenniallegumes are sometimes retained in farmers’fields and are just beginning to be incorporatedas hedgerow intercrop or alley crop systems.Giller, McDonagh, and Cadisch (1994) concludethat biological N fixation from legumes cansustain tropical agriculture at moderate levelsof output, often double those currentlyachieved. Under favorable conditions, greenmanure crops generate large amounts oforganic matter and can accumulate 100-200 kgN/ha in 100-150 days in the tropics.

Legumes remain marginal in many of themaize-based systems of the region, however,for several reasons. Low P levels in the soilsinhibit legume growth, and so at a minimum Pmust be added. Much of the work underlyinglegume-based technologies has been done onresearch stations. Insufficient account has beentaken of the need to tailor these technologies tofarming circumstances where labor is in shortsupply. The fertilizer needed to “kick start” thesystem may be too costly or unavailable, andthere are often difficulties in obtaining legumeseeds (e.g., Giller, McDonagh, and Cadisch1994). Finally, the family may not be able torelease land from staple food crops.

There is often a direct conflict between the needto assure today’s food supply and the need toassure tomorrow’s food supply by building upsoil fertility over a long period. Farmersdiscount the value of a benefit that will only beachieved several years from when investmentsare made. The most suitable legumes, from thesoil fertility perspective, are often the mostdifficult for the farmer to adopt. Broadlyspeaking, the larger the soil fertility benefitfrom a legume technology is likely to be, thelarger the initial investment required in laborand land, and the fewer short-term foodbenefits it has.

Grain legumes. Grain legumes have the fewestadoption problems and are widely grown byfarmers, mainly for home consumption of theseed and sometimes leaves. However, the moreproductive (high harvest index) grain legumesadd relatively little organic matter and N to thesoil, since much of the above-ground drymatter and almost all the N is removed fromthe field in the grain (see Giller, McDonagh,and Cadisch 1994). Species that combine somegrain with high root biomass and shoot-leafbiomass, such as pigeonpeas (Cajanus cajan)and dolichos beans (Dolichos lablab), offer auseful compromise of promoting farmeradoption and improving soil fertility (K.E.Giller, pers. comm.).

Carr (1994) reports that, on severely depletedsoils in Malawi, soybeans (Glycine max) willproduce more calories per unit of land thanunfertilized maize, in addition to fixing N fromthe atmosphere. Also in Malawi, Kumwenda(1995) reported average soybean yields of 2,200and 860 kg/ha, respectively, in monocultureand intercropping from a self-nodulating(promiscuous) variety, Magoye. Promiscuoussoybeans are attractive to smallholders becausethey do not have to be inoculated withRhizobium spp. bacteria to fix N, and they also

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have good root and above-ground biomass.Magoye is grown very widely in Zambia and isnow grown by thousands of smallholders inMalawi, but Malawi has not yet approvedrecommendations for its use. Zimbabwe doeslittle soybean research for smallholders. Thebias in regional soybean development istowards varieties with high grain yields, whichare favored by large-scale producers whoseinterest in soil fertility improvement issecondary.

Legume intercropping. Intercropping, in whichtwo or more crops are grown mixed togetheron the same ground for all or most of their lifecycle, is a widespread, traditional Africanagricultural practice (Andrews and Kassam1976). Legumes in intercropping systems cancontribute some residual nitrogen to thesubsequent crop (Willey 1979). However, low-growing legumes are often shaded by tallercereals (Dalal 1974, Chang and Shibles 1985,Manson, Leughner, and Vorst 1986), and undersmallholder management in low-fertilityconditions, poor emergence and growth of theintercropped legume is common. This limitsthe N and organic matter contribution of thelegume on farmers’ fields to levels well belowthe potentials found on research stations(Kumwenda et al. 1993, Kumwenda 1995).

One of the more promising intercrops is late-maturing pigeonpea. Even though earlygrowth of the legume is reduced when it isintercropped with maize, pigeonpeacompensates by continuing to grow after themaize harvest and produces large quantities ofbiomass (Sakala, 1994). In Malawi, Sakala(1994) reported a pigeonpea dry matter yield of3 t/ha from leaf litter and flowers whenpigeonpea was intercropped with maize.Pigeonpea is easily intercropped with cerealsand, even if the seed is harvested for food, theleaf fall is sufficient to make a significant

contribution to N accumulation. Thedisadvantage is that pigeonpea is highlyattractive to livestock and impractical to growwhere livestock are left to roam the fields freelyafter harvest, a common practice in manyAfrican smallholder systems.

The importance of intercrops in denselypopulated regions is widely recognized.Intercrops have a stabilizing effect on foodsecurity and enhance the efficiency of land use.However, in semiarid areas, plant densities(and thus potential yield per hectare) must bereduced in intercropping systems (Shumba,Dhliwayo, and Mukoko 1990). Those authors,working in southern Zimbabwe, found thatcowpea-maize intercrops greatly reduced thegrain yield of maize in dry years. Natarajanand Shumba (1990), reviewing intercroppingresearch in Zimbabwe, observed that cereal-legume rotations appear to offer greaterprospects of raising the yield of cereals than dointercrops. Whereas maize benefits from beinggrown after groundnuts (Arachis hypogaea),maize-groundnut intercrops often reducemaize yield (see Hikwa and Mukurumbira1995). Cowpea-maize (Vigna unguiculata)intercrops yield better than either maize orcowpea sole crops on a land-equivalent basis inwetter areas of Zimbabwe (Mariga 1990).

Legume rotations. Legume rotations are animportant practice for restoring soil fertility onlarger land holdings. Rotations allow cropswith different rooting patterns to use the soilsequentially, reduce pests and diseases harmfulto crops, and sustain the productivity of thecropping system. The amount of N returnedfrom legume rotations depends on whether thelegume is harvested for seed, used for forage,or incorporated as a green manure. In Malawi,MacColl (1989) estimated net N of 23-110 kg/ha from pigeonpeas, 23-50 kg/ha from dolichosbeans, and 25 kg/ha from groundnuts.

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In Nigeria, Jones (1974) and Giri and De (1980)estimated 60 kg N/ha from groundnuts.

The yield response of a cereal crop following alegume can be substantial. In Malawi, MacColl(1989) showed that the grain yield of the firstmaize crop following pigeonpea averaged2.8 t/ha higher than the yield of continuousmaize that received 35 kg N/ha each year.Mukurumbira (1985) showed large maizeyields in Zimbabwe following groundnuts andbambara nuts (Voandzeia subterranea), withoutsupplemental inorganic nitrogen. Similarstudies in Tanzania by Temu (1982) found thatmaize yields after sunnhemp (Crotolaria spp.)were 3.65 t/ha when residues were removedand 4.82 t/ha when they were incorporated.The incorporated residues were equivalent toan application of 80 kg N/ha from inorganicfertilizer. Supplementing sunnhemp greenmanure by incorporating 40 kg N/ha gave ayield of 6.83 t/ha, which was equivalent to anapplication of 160 kg/ha of inorganic Nfertilizer.

Improved fallowing with legumes. Naturalshort fallowing of overworked land inZimbabwe results in little or no increase in soilfertility (Grant 1981). Improved fallows, usingSesbania sesban as a way of adding significantamounts of N and organic matter to soil, havebeen evaluated in Eastern Province, Zambia,where short, two- to three-year fallows arecommon. On the research station, maizeyielded between 3 and 6 t/ha of grain for eachof four years following a two-year improvedfallow, compared to a yield of 1-2 t/ha in theunfertilized control (Kwesiga and Coe 1994).From these data, Place, Mwanza, and Kwesiga(1995) calculated that when inorganic fertilizeris not used — the common practice in easternZambia since fertilizer subsidies were removed— it is profitable for farmers to invest in theimproved fallow. The use of improved fallows

avoids the competition effect between trees andcrops (Kwesiga and Coe 1994). But where landis limiting, the feasibility of improved fallowsystems remains unproven.

Agroforestry. Agroforestry refers to land-usesystems in which woody perennials (such astrees and shrubs) are grown in association withherbaceous plants (such as crops or pastures)and/or livestock in a spatial arrangement, arotation, or both, and in which ecological andeconomic interactions occur between the treesand other components of the system (Young1989). Given the widespread decline in soilfertility, the use of leguminous, multipurposetrees for improving soil fertility has been amajor thrust of agroforestry research in theregion.

Alley cropping, sometimes referred to ashedgerow intercropping, was developed in thelate 1970s at the International Institute ofTropical Agriculture (IITA) and is the best-known agroforestry system developed forimproving soil fertility (Kang, Reynolds, andAttah-Krah 1990). The underlying assumptionof this technology is that moisture andnutrients below the roots of annual crops willbe used by the more deeply rooted tree crop.The tree crop is pruned to supply nutrients tothe soil, which are used by the shallowly rootedannuals. Jones et al. (1996), Wendt et al. (1996),and Bunderson et al. (1991) showed that theapplication of Leucaena leucocephala leafprunings in an alley cropping system raisedmaize grain yield and increased soil pH;organic C; total N; S; and exchangeable calcium(Ca), Mg, and K.

Important aspects of agroforestry areproblematic, however. Inorganic P may beneeded to realize increased maize yields.Leucaena (the most widely researchedhedgerow species) suffers from susceptibility to

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termite attack at the seedling stage, severedefoliation by the recently arrived LeucaenaPsyllid, and poor biomass production underlow fertility and on low pH soils. Saka et al.(1995) have estimated that the cost ofproducing N from Leuceana biomass iscomparable to that from inorganic sources. Thetechnology is labor intensive and managementsensitive. Trees and associated crops cancompete for moisture, nutrients, and light(Mbekeani 1991, Ong 1994). Observationssuggest that competition for soil moisture isparticularly acute at the beginning of the rainyseason before moisture reserves have built up.Without a better understanding of thecompetitive effects between trees andassociated crops, especially those effects belowground, the potential of alley cropping isunproven at the farm level.

Some progress has been made on aspects ofthese problems. Research has identifiedalternative species that are better adapted andproduce more biomass than L. leucocephala(Bunderson 1994). Gliricidia sepium and Sennaspectabilis have both shown potential toproduce more biomass in a wider range ofecologies.

Another agroforestry technology that may offersome promise is Faidherbia albida, a vigorousleguminous tree long used by African farmersfor improving crop yields where the tree isnaturally abundant. The species has thecharacteristic, unique among African savannatree species, of retaining its leaves in the dryseason and shedding them at the onset of therains. The resultant fine mulch of leaf litterdecomposes rapidly, enriching the topsoil inplant nutrients and organic matter. Saka et al.(1994) have described how natural stands of thetree have been used in maize productionsystems in Malawi. Although farmers

recognize the value of F. albida, the tree has notbeen integrated systematically into maize-growing areas.

Cereal residues and animal manure — Theburning of crop residues remains common.Where it is a deliberate farmer practice (mainlyin areas with few livestock), burning is used torelease nutrients quickly, ease landpreparation, and reduce pest and diseasepressure. Although the nutrient content ofmaize stover is relatively low, stover cancontribute to the productivity of the soil. Suchresidues must be managed carefully, however,because N can be immobilized at the time ofpeak maize N requirements, resulting in poorcrop growth (Nandwa, Anderson, and Seward1995); this fact is well known to farmers.

In unimodal rainfall areas where stover tendsto break down slowly in the soil, and on sandysoils where soil N is very low, maize stover isusually fed to livestock. As well as keepinganimals alive, this practice helps cycle residuesin a way that makes them more beneficial to thecrop. In smallholder areas where cattle arecommon, as in parts of Zimbabwe, farmersoften apply cattle manure to fields that will beplanted to maize. Losses of N from suchsystems are often high, however. Cattle manureis applied in a dried, aerobically decomposedform, often with a high sand content and an Ncontent that is frequently less than 1.2%(Mugwira and Mukurumbira 1984). Manure isbroadcast and plowed into the soil beforeplanting. Survey discussions with farmers andinformal assessments indicate that farmersapply around 8-20 t/ha every three to fiveyears (Mugwira and Shumba 1986). Researchshows that the most efficient use of manure isto combine it with some inorganic fertilizer(Murwira 1994). This is a common practice offarmers. Station-placement or dribbling into theplanting furrow, rather than broadcast

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application, are promising ways of increasingthe crop yield benefits from cattle manure (e.g.,Munguri, Mariga, and Chivinge 1996).

Improving maize genotypes forsoils with low fertilityIn addition to finding ways of altering the soilto better support maize crops, researchers arealso developing maize genotypes that performbetter when soil fertility is limiting. A slightimprovement of N-use efficiency has beenreported in tropical maize, with prospects offurther gains (Lafitte and Edmeades 1994a,1994b). At CIMMYT in Mexico, three cycles offull-sib recurrent selection for grain yield underlow soil N, while maintaining grain yield underhigh soil N, were conducted in a lowlandtropical population, Across 8328 (Lafitte andEdmeades 1994a, 1994b). This resulted in a per-cycle increase in grain yield under low N of75 kg/ha (2.8%), with similar yieldimprovements under high N (Lafitte andEdmeades 1994b). If these improvementscontinue over another three to five cycles ofselection, they will be substantial. At CIMMYTin Zimbabwe, similar work in populationZM609, adapted to midaltitude areas ofsouthern and eastern Africa, led to large initialgains in N-use efficiency (Short and Edmeades1991), but recent work has been inconclusive(Pixley 1995).

Also, significant progress in using full-sibrecurrent selection to develop tropical maizefor tolerance to high Al3+ saturation in acidicsoils is reported by Granados, Pandey, andCeballos (1993). These materials should betested and modified to suit African conditions,and breeding work should be established todevelop maize that yields well in soils thathave high concentrations of H+ but withoutAl3+ or Mn2+ toxicity. Breeding for tolerance tomicronutrient deficiencies may be anotherworthwhile long-term goal.

Agronomists and social scientists continue tohave a role in encouraging breeders to perseverewith work on soil fertility issues. Most breedersare more comfortable with breeding to overcomebiotic constraints, where they feel they can makemore progress. However, the edaphicconstraints found on smallholders’ fields need tobe addressed. There is an urgent need forimproved germplasm adapted to nutrientdeficiencies and other edaphic stresses. Most ofthe gains achieved in N-use efficiency throughbreeding have come from improved Nutilization to produce more biomass and grainyield with no increase in total N uptake (Lafitteand Edmeades 1994b). Nevertheless, there issome concern that future genotypes bred for lowsoil fertility may gain their advantage fromextracting more micro- and macronutrients fromthe soil. The outcome of such a strategy isuncertain, and therefore it is important not torely solely on crop improvement.

The way forwardThe technologies needed to manage soil fertilityin southern Africa do not differ from thosedeveloped for other parts of the world.Inorganic fertilizers are a key element of fertilitymanagement, because the need for addedexternal nutrient inputs is inescapable, but suchfertilizers should not be the sole source ofnutrients. Some sources of organic fertility,mainly based around the use of legumes in thecropping system, can usefully complementinorganic fertilizers. However, importantpractical questions about both sources of fertilityunder smallholders’ circumstances remainunanswered: the optimum use of small amountsof inorganic fertilizers, the best combinations oforganic and inorganic fertilizers, how to producesufficient amounts of organic manures underlow-fertility conditions, the best managementcompromises in the use of labor between criticalseasonal tasks, and adjusting fertilitymanagement according to seasonal rainfall and

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other external factors. This deficiency ofinformation persists despite some adaptiveresearch on these issues in the 1980s and early1990s (e.g., Waddington 1994).

Yet these are the very questions thatsmallholders seek to answer. Typically,farmers are looking for means of combiningthese inputs and employing them in ways thatminimize the requirements for additional cash,labor, and land. Little past or ongoingexperimentation exists to guide them throughthe choices, and extension offers little counsel.

From the previous discussion, it is clear thatflexible soil fertility recommendations arerequired that better address actual nutrientdeficiencies, take advantage of croppingsystem opportunities, are efficient under thehighly variable rainfall regime faced by mostsmallholders, and are compatible with farmers’socioeconomic circumstances. Combinations oftechnologies (involving organic and inorganicsources), often with each component employedsuboptimally, will be needed. Organicmanures are highly variable and usually inshort supply. Mixing high-quality organicsources with inorganic fertilizer cansubstantially improve nutrient-use efficiencyand crop productivity. The resultant practiceswill be practicable and profitable, and thuscandidates for wider adoption.

Transferring experience in fertilitymanagement from other regions of the worldrequires not only adaptation but also a muchgreater understanding of the processes throughwhich fertility can be managed under Africanconditions. This concurrent requirement foradaptive research as well as basic processresearch is taken up in the next section of thispaper.

Linking Adaptive and ProcessResearch to Improve TechnologyDevelopment and Dissemination

African crop management research requires twocritical types of research to be conducted in acollaborative, highly focused manner:

• basic process research for a betterunderstanding of the soil fertility cycle (itsinputs and its losses) on African farms, toensure that technology will be effective, and

• adaptive research with farmers and otherclients, to ensure that an integrated sequenceof activities follows up on findings from basicresearch.

The methods for each type of research aredifferent. It is rare for scientists working inprocess research to have a full grasp of the skillsneeded for adaptive research, and vice versa.Fertility changes have long-term effects onproductivity, but it is important to remember thatchanges in agriculture are typically incrementalrather than spectacular. Only through aconsistent, long-term effort will scientistsunderstand the changes that are taking place. Toensure that the research agenda remains fixed onimportant productivity problems and does notget sidetracked into equally challenging but lessrelevant avenues, these researchers must share acommon vision of the problems faced by farmers.

Many of the key characteristics of adaptiveagricultural research are well described in theliterature (for example, see Tripp 1992). Wepropose to build on the foundation of adaptiveresearch by adding a long-term perspective, inwhich investigation, review, and interaction withproducers and other concerned parties elicit acoherent research strategy running consistentlyover time. The next section provides one exampleof such a process, which is already underway.We then proceed to show how progress in

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applied research requires an underpinning ofhigh-quality, carefully prioritized basic studies.

A case study in applied research:Overcoming micronutrientdeficiencies for maize in Malawi6'

Research on the relief of micronutrientdeficiencies for maize in Malawi exemplifiesthe commitment needed for “successful” soilfertility research. Over three seasons from 1990to 1992, Conroy (1993) showed thatsmallholders following current fertilizerrecommendations — a single blanket

recommendation of 92 kg N and 40 kg P2O5 perhectare was standard throughout Malawi —obtained only about 3 t/ha of maize grain, eventhough farmers planted hybrids with yieldpotentials exceeding 10 t/ha. More than 40% ofthe smallholders who applied fertilizer atrecommended rates failed to cover the cost offertilizer application.

Table 2 shows the research sequence andoutputs. The process embraced soil chemicalanalysis, investigative trials with missingmicronutrients at a relatively small number of

Table 2. The relief of micronutrient deficiencies on maize in Malawi: an example of a long-term research process

1987 - 89 1989 - 90 1990 - 91 1991 - 92 1992 - 93 1993 - 94 1994 - 95 and onwards

Activities and methods* Review * Missing nutrient trials at 10 on-farm * Nutrient * Map regional nutrient deficiencies

past trials and research station sites in supplement * Formulate new basal fertilizers and distributeand conduct selected areas treatments * Collect and analyze soil from 3,000 geo-farm surveys * Soil and tissue chemical to on-farm referenced sites throughout Malawi

analysis at sites demonstrations * Verification trials of new fertilizers at several* Soil analysis hundred on-farm sites, involving farmers

at 400 sites inCentral Malawi * Use GIS to map sites

* Better target verificationsto sites deficient in S and Zn,involve extension and farmers

* N response trials at siteswhere micronutrientdeficiencies satisfied

Key outputs* Micronutrient * Regional deficiencies of S, Zn, B, * Near universal * Good yield * Optichem to produce com-

deficiency and K found S and Zn deficiency response to pound fertilizer with 1Znlikely cause * Yields increase by 40% over standard N-P in some ADDs basal fertilizers * Include results from betterof yields <3 t/ha when micronutrient deficiencies satisfied * Confirmed containing S targeted verifications inwith current * P not needed at some sites while others yield responses * Responses at new recommendationsN-P-K need more than current recommendation * Optichem to low-Zn sites * Results from responserecommendation * More verification with farmers needed produce 20:20:5+4S were poor; economics

+0.1Zn and 0.1Zn is * Results from N response15:10:5+4S+0.1Zn insufficient trials where micronutrients

relievedOrganizations* Maize and Soils Commodity Research Teams in the Department of Agricultural Research, Ministry of Agriculture* Smallholder farmers

*FAO/Ministry of Agriculture/UNDP project*Fertilizer maker (Optichem)

*Ministry of Agriculture Extension Service

Note: ADDs = Agricultural Development Divisions; GIS= geographic information system; FAO = Food and Agriculture Organization;UNDP = United Nations Development Programme.

6 The work synthesized here is the result of efforts by many persons and organizations in Malawi. In particular, creditfor much of this research goes to John Wendt and Richard Jones, Rockefeller Foundation Post-doctoral Scientistsattached to the Department of Agricultural Research in Malawi from 1989 to 1993.

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on-farm sites, and the formulation of newfertilizer blends (including Zn and S) with afertilizer manufacturer. This last step wascombined with simple on-farm verifications ofincreased yield and profitability when the newformulations were used. The on-farmverifications actively involved the extensionservice and farmers.

In 1987, informal farmer surveys indicated thatlow yields were not generally caused by poorplanting or weeding or adverse climaticconditions. Farmers had been growing maizecontinuously (sometimes with a minor legumeintercrop) with minimal rotation for manyyears. Researchers hypothesized that low yieldsmight result from deficiencies of nutrients otherthan N and P. Two initial research goals wereidentified:

• to determine yield response, in a given soiltype and agroecological zone, to fertilizersthat addressed local soil nutrient deficiencies;and

• to determine the relationship of soil fertilityanalytical values to maize yield response tofertilizer added (this relationship isinfluenced by climate, soil type, and profile).

The literature and other sources of informationestablished that the absence of one or more of arange of nutrients (besides N and P) had thepotential to depress yields significantly. Severalof these potential nutrient deficiencies werediscarded and not researched: either thedeficiency was unlikely, was already addressedin the existing fertilizer formulation, or wasimpractical to deal with in the Malawiancontext.

In 1989, researchers initiated a series of on-farmtrials to evaluate deficiencies of N, P, K, S, Zn,and B at several sites throughout Malawi. A“missing nutrient, minus one” trial design was

used to evaluate the relative contribution ofeach nutrient to maximizing yields. To keep theclients’ needs sharply in focus, researchersconducted much of their work in smallholders’fields. New methods included tissue sampling,in which ear leaves were taken from all plots atsilking and analyzed for N, P, Ca, Mg, K, S, Zn,Cu (copper), Mn, Fe (iron), and B. Data from thesoil and plant analyses were correlated withyield data to determine minimum soil analyticalcriteria for the elements studied.

There was a regular process of review. Thetreatments and treatment methods evolvedfrom year to year, based on experience fromprevious years. By 1991/92, a general reviewconcluded that yield data indicated regionaldeficiencies of B, Zn, S, and K. In deficientregions, average yields improved by 40% overyields obtained using the existing N and Papplication when the deficiencies were satisfied.Lime applications were necessary at some sites.Soil and plant analyses showed P applicationwas unnecessary at some sites, while at othersites the recommended P fertilizer rate wasinsufficient.

To refine these observations, the research teamcollaborated with a fertilizer demonstrationproject run by the extension service and FAO. In1992/93, micronutrient supplement treatmentswere added on selected extension fertilizerdemonstrations throughout the country. Ananalysis of soil samples from 400 smallholdersites enabled researchers to develop preliminarymaps of areas with S, Zn, K, Cu, and Pdeficiencies for maize in Malawi (Wendt, Jones,and Itimu 1994).

The next step was to work with a local fertilizercompany to produce practical fertilizer blendsthat addressed these regional deficiencies. Twotypes of fertilizers were produced in 1993/94; in1994/95, based on further experience, another

19

formulation was produced. Concurrently, thecharacterization of nutrient deficiencies wasgreatly expanded to refine the nutrientdeficiency maps. More than 3,000 soil sampleswere collected and analyzed for pH, P, Ca, K,Mg, Zn, Cu, B, soil organic matter, and soiltexture. The sample locations were geo-referenced (elevation, longitude, and latitude)to develop a computer database that could beused with a geographic information system(GIS). Farm management information was alsocollected. Trials were conducted from 1993/94onwards to verify the new fertilizerformulations under farmers’ conditions anddemonstrate more efficient methods for usingfertilizer. This work was done in conjunctionwith the extension service, with guidance andassistance from the Department of AgriculturalResearch. In 1994/95, work was started todefine new response curves for N and P withhybrid maize where the micronutrients wereadded. The fertilizer company has advertisedthe new 20:20:5+4S+0.1Zn fertilizer andprocedures are in place to incorporate newfertilizers into standard recommendations.

Clearly blanket fertilizer recommendations areinadequate. They result in the inefficient use ofan expensive, usually imported, commodity,which is costly for the farmer and for thenation. This is uncontroversial, but progress indealing with this evident and crucial problemhas been slow. This example from Malawiillustrates how progress is possible withmodest resources but a clear sense of direction.Researchers exploited the potential of modernfertilizer blending systems to produce small“runs” of fertilizer to given specifications.Through a focused program of research andverification, fertilizer recommendations can bedeveloped for localized areas at a surprisinglyreasonable cost, and through databasemanagement techniques, theserecommendations can be refined further.

Basic process researchThe challenge and the tools — The appliedresearch outlined in the preceding section mustbe underpinned by high-quality researchaimed at comprehending the basic processesunderlying nutrient flows in tropical soils.Nutrient budgets and process-level researchtrack the consequences of crop managementstrategies in smallholder farming systems. Thegoal is to synthesize our knowledge ofprocesses involved in nutrient cyclingefficiency, which will enable us to predictwhich agronomic technologies enhance yieldpotential over the long term. The challenge isenormous, because detectable changes in soilorganic matter and other soil fertilityparameters occur very slowly. For example, ina hedgerow intercrop trial at Bunda College ofAgriculture, University of Malawi, soil organicC was not altered after 10 years of widelydiffering residue input rates (Snapp andMaterechera 1995).

The first step towards further improvingorganic matter technologies is to quantifynutrient losses and inputs at different scalesand extrapolate among them. Typical scalesinclude the plot level, the farm level, thewatershed level, and the regional level (Frescoand Kroonenberg 1992). The definitive test forevaluating the effects of technologies on soilfertility is the measurement of yields over thelong term. Studies conducted over decades in asystematic, rigorous manner are clearly neededin sub-Saharan Africa and for the tropicsgenerally. However, because farmers needimproved technologies now, faster methods arerequired. Regional assessments of soil nutrientstatus and losses have necessarily been almostentirely based on extrapolation of plotestimates (Smaling 1993), but results have notbeen reliable.

20

Several new methods hold considerablepromise for assessing nutrient flows across theheterogeneous landscape of smallholder farmsin the tropics (Barrios, Buresch, and Sprent1994; Jones, Snapp, and Phombeya 1996; Parton1992; Snapp, Phombeya, and Materechera1995). Powerful tools of the trade includenutrient monitoring, new methods in soilanalysis, modeling, and networked or chrono-sequence trials to allow rapid insight into soilfertility processes (Anderson and Ingram 1993;Jackson et al. 1988; Parton 1992; Snapp,Phombeya, and Materechera 1995).Investigations must be conducted onrepresentative sites of well-characterizedagroecosystems. Networked trials andstandardized analytical methods are needed toquantify the consequences of differentmanagement regimes for the soil resource base(Anderson and Ingram 1993). This type of basicresearch could potentially support a major shiftin tropical agronomy from empirical testing todesigning crop management strategies. To besuccessful, this research requires a continuingcommitment to building bridges among fieldssuch as agronomy, ecology, soil biology,chemistry, and physics.

Nutrient budgeting — Nutrient budgeting canbe used to develop improved ways of usingavailable nutrients. We have underlined theimportance of organic matter management onAfrica’s leached and depleted soils. Usingconventional methods from temperate zones, itis difficult to maintain SOM. Substantialamounts of organic inputs are needed toenhance SOM in tropical cropping systems(Jenkinson 1981). Recent findings suggest thatsmall additions of high-quality organicmaterial can increase nutrient cyclingefficiency. Such material is high in available Nand provides a source of energy (availablecarbon) to soil microorganisms. Enhancedactivity of soil microbes can increase nutrient

turnover rates, improving nutrient availabilityto crops while minimizing nutrient losses fromleaching and volatilization (De Ruiter et al.1993; Doran et al. 1987; Granastein et al. 1987;Ladd and Amato 1985).

These findings suggest an opportunity in thetropics to use active microorganismpopulations to buffer (or reduce nutrient lossesfrom) low-input cropping systems. Althoughthe pool of inorganic nutrients is small in suchsystems, the nutrient supply may be sufficientto support crop growth because of thecontinual re-supply of nutrients by microbiallymediated turnover rates. Nutrient losses dueto leaching and volatilization are reduced(Figure 2). Crop nutrient budget methodology(after Jackson et al. 1988), focusing on N losses(N is the nutrient most limiting to growth, andmost vulnerable to losses from smallholderfarms in southern and eastern Africa), is beingdeveloped to test this theory.

Related process studies have recently beeninitiated in Malawi, including 15N isotopelabeling, to quantify the effects of smallamounts of organic residues applied withinorganic nutrients under field conditions(Jones, Snapp, and Phombeya 1996).Researchers in Zimbabwe have undertaken arange of intensive studies of N efficiency,using 15N isotope and novel N monitoringtechniques (TSBF 1995, Tagwira 1995). Whilethe results from these studies remainpreliminary, the initial findings are exciting.

Development of new methods — Newtechniques have recently been developed forseparating SOM into fractions that may bebiologically meaningful and that appear tohave predictive value for agronomists andland managers. Physically based isolation ofSOM fractions can be achieved rapidly andeasily by sieving soil and separating SOM on

21

essential for efficient nutrient acquisition,particularly for mobile nutrients such as nitrateN. Nitrogen losses from tropical croppingsystems have not been well documented butare expected to be substantial, exceeding 30-70% of N inputs. Major N losses are thought tooccur early in the cropping season as a result ofhigh initial mineralization rates, inorganic Naccumulation during the dry season, andlimited root growth of young crop plants(Myers et al. 1994).

Understanding root behavior is also essential tominimize competition associated withintercropping technologies. Several importantagroforestry systems are based on theassumption that the trees reduce nutrient lossesby scavenging nutrients at a depth lower thanthe crop roots (Young 1989). Preliminaryfindings from studies of two significant maize/perennial legume intercrop systems for Malawi

the basis of size (Cambardella and Elliot 1994,Christensen 1992). Early findings are that afraction of SOM known as the light/large (LL)fraction provides a good indicator of activeSOM.

Use of SOM fractionation, and measurement ofLL-associated organic C and N, are beingevaluated in Zimbabwe, Kenya, and Malawi(Barrios, Buresh, and Sprent 1994; Okalebo,Gathua, and Woomer 1993; Snapp, Phombeya,and Materechera 1995). Organic C in the LLfraction was higher in two Malawian soilsamended with G. sepium or L. leucocephalacompared to a control (continuous maize withno fertilizer) or an intercrop with a legume thatdoes not fix N, S. spectabilis (Saka et al. 1995).

Root studies — Roots play an important role inregulating nutrient cycling efficiency. Avigorous, effective crop rooting system is

Figure 2. The role of high-quality organic inputs in improving the efficiency of inorganicfertilizer use.Note: Rapid cycling between inorganic N and soil microbe N allows the plant to take up N without a large pool ofinorganic N, which is vulnerable to leaching.

Inorganic Inorganic + Organic

Soilorganicmatter

Soilmicrobe

pool

Plant uptakePlant uptake

Soilmicrobe

pool NO3- NH4+NO3- NH4+

Fertilizer

Highquality

organics

Leaching andvolatilization losses

Leaching andvolatilization losses

Soilorganicmatter

Fertilizer

Substrate

22

— S. spectabilis and G. sepium alley croppedwith maize — suggested that ridge planting ofmaize (a widespread practice of Malawiansmallholders) reduced competition betweenmaize and the perennial legumes (O. Itimu andK.E. Giller, pers. comm.). However, the datastrongly pointed to intense competitionbetween crop and tree roots and to onlymodestly deep rooting of the perennials. Thesoil environment influenced rooting patterns toas great a degree as genotype. Thus reducingnegative interactions between tree roots andannual crops, and enhancing benefits from treeroots, may be fundamental to the success of thetechnology (Giller, Itimu, and Masamba 1996).

Nutrient release synchrony — Anotherapproach advocated for increasing nutrientcycling efficiency is to synchronize nutrientrelease with crop demand (Anderson andIngram 1993). Synchronizing the release ofnutrients from organic materials with a crop’srequirement for nutrients can increase nutrientcycling efficiency (Myers et al. 1994). Thiscentral hypothesis of the Tropical Soil Biologyand Fertility Program (TSBF) suggests thatorganic inputs of varying quality can be usedto manipulate nutrient supply. Laboratoryincubation studies have shown that high-quality residues (e.g., narrow C/N ratio, lowpercent lignin) supplied in conjunction withlow-quality residues (e.g., wide C/N ratioand/or high lignins) can provide a continuousnutrient supply, with N being released fromhigh-quality residues first (O. Itimu and K.E.Giller, pers. comm., 1995; Snapp, Phombeya,and Materechera 1995; TSBF 1995). Preliminaryfield data support these findings. For three outof four Malawi soils, levels of inorganic N wereenhanced in soil amended with high-quality G.sepium residues, compared to controls (no

fertilizer or organic inputs) or to soil amendedwith moderately high quality residues of S.spectabilis (Snapp, Phombeya, and Materechera1995). Nevertheless, synchronizing nutrientrelease with nutrient demand using organicresidues is technically demanding. Just howpracticable this is for farmers on their fieldsevery year has yet to be shown.

The quality of residues is difficult to evaluate.The SOM fractionation methods discussedearlier may provide one means of assessing thequality of residue after it is incorporated intosoil; most important, these methods may alsoserve to quantify the consequences for soilquality. Preliminary indications are that plantswith high lignins, polyphenolics, and otheranti-quality factors may not release nutrientsfor many growing seasons, and thus theseresidues may be undesirable to use as organicsoil amendments (Myers et al. 1994). Studieshave been initiated in Zimbabwe and Malawito test the synchrony hypothesis under fieldconditions (TSBF 1995, Snapp and Materecha1995).

Conclusion — We have emphasized ways inwhich types of technologies (organic andinorganic sources of soil fertility) and types ofresearch (adaptive and basic process research)must be linked to ensure that more rapidprogress is made in developing soil fertilitypractices that smallholders can adopt. Now wefocus on another set of important links intechnology development: the interactionsbetween soil fertility technologies and otherinputs and management factors in the croppingsystem.

23

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Exploiting Interactions of SoilFertility Technologies with

Other Inputs and ManagementFactors

In southern Africa, the defining feature of theecology is the dry season, which lasts seven toeight months. Because the dry season is so long,important farm operations, particularlyplanting, weeding, and fertilizing, areconcentrated in the critical early weeks of therainy season. The options for addressing soilfertility problems are influenced by cropchoices, the season, the climate, and a host ofother factors, some of which farmers cancontrol or modify, and some of which theycannot. Thus it is the interaction of soil fertilitytechnology with other, possibly more readilyadoptable, farmer inputs and managementpractices that needs particular consideration.Interactions can be expected with weed controlpractices, with moisture availability, withfertilizer-responsive and -efficient maize, withlabor, and with draft power.

Interactions with weed managementKabambe and Kumwenda (1995) examined theinteraction between weed growth andfertilizer-use efficiency in Malawi. They foundthat farmers who weeded twice at the criticalperiods for maize achieved a higher yield, withhalf the amount of fertilizer, than farmers whoweeded only once (Figure 3).

Where animal draft power is available, theoptions for exploring interactions with weedmanagement methods increase (see Low andWaddington 1990). Results from Zambia showthat combining basal and topdress fertilizer,applied when weeding 20-cm-tall maize,resulted in a savings of six person-days perhectare during the peak demand period forfamily labor. The practice also gave a 19% yieldincrease compared with the standard farmer

practice of a basal application just afterplanting, followed by late weeding andtopdressings (Low and Waddington 1990;1991). These results were developed intoseparate recommendations for ox-cultivatorsand for farmers who used hand hoes forweeding. Ox-cultivators were advised to weedwith oxen two weeks after emergence whilecovering the mixed basal and topdress fertilizer(applied immediately beforehand) in the sameoperation; hand weeding on the crop rowwithin the subsequent two weeks was alsorecommended. Hand-hoe weeders wereadvised to combine the first hoe-weeding witha mixed basal and topdress fertilizerapplication, beginning ten days afteremergence. A second weeding would followtwo weeks later.

Soil fertility decline may cause weeds (andinsect pests and diseases) to build up andthereby indirectly affect crop production. Awell-known example of such an interaction isthe parasitic weed, Striga spp., which tends tobuild up when soils are depleted, althoughonce it is established it is hard to controlthrough improved soil fertility alone. Data

Mai

ze g

rain

yie

ld (

t/ha)

5

4

3

2

1

0Weeding Weeding Weeding Noat 21,45, at 21 at 28 days weedingand 54 and 45 after

days after days after plantingplanting planting

Figure 3. Effect of weeding frequency and Napplication on maize grain yield.Source: Kabambe and Kumwenda (1995).

0 kg N/ha45 kg N/ha90 kg N/ha

24

from long-term trials in Kenya have shown thatincorporated crop residues play an importantrole in reducing Striga parasitism (Odhiamboand Ransom 1995).

Interactions with moistureThe climate of southern Africa means that lackof moisture frequently constrains maize yieldsand yield response to fertilizer. The efficiency(measured through grain production) of bothwater use and N use is raised when both waterand N are in adequate supply. But the high riskof poor response to fertilizer in dry years is amajor reason why most farmers in semiaridareas use little or no fertilizer. An overdepen-dence (as in Zimbabwe) on developing site-specific fertilizer recommendations through soilchemical analyses alone (Grant 1981,Metelerkamp 1988), and the concept of regularmaintenance dressings (for K and P), haveresulted in unrealistically high and rarelyadopted recommendations for smallholderfarms, especially in semiarid areas. Uncertaintyexists over appropriate N-P-K fertilizerrecommendations for semiarid areas. The utilityand economics of fixed recommendations forsuch areas is increasingly questioned (e.g.,Mataruka, Makombe, and Low 1990; Shumba etal. 1990; Piha 1993; Page and Chonyera 1994).

The practices of smallholders in Zimbabwereflect the need for substantially revisedfertilizer recommendations. The frequency withwhich these farmers apply inorganic fertilizerand the amounts they apply are stronglyinfluenced by seasonal rainfall. Almost allsmallholder farmers apply some inorganicfertilizer to maize in the wetter areas (NaturalRegions II and III). In a survey of ten communallands in such areas, Waddington et al. (1991)found that farmers applied an average of 65 kgN/ha to their earlier plantings of maize. But forlate plantings (of lower yield potential), N ratesfell to about 60% of those for earlier plantings.

In semiarid areas, the use of inorganic fertilizeris low. Rohrbach (1988) found that in ChiviCommunal Area of Zimbabwe (which isrepresentative of these conditions), fewer than10% of farmers regularly applied fertilizer(usually low rates of topdress N). Data fromthe 1991-94 seasons in Gutu (Natural RegionIV) Communal Area show 80% of farmersusing an average of 19 kg N/ha on fields thatwere monitored. In Chivi (Natural Region IV-V), only 23% of farmers applied fertilizer at anaverage rate of 8 kg N/ha (DR&SS/CIMMYT,unpublished). In intermediate rainfall areassuch as Shurugwi-Chiwundura and Wedza,most farmers (79-91%) use topdress N butfewer than half applied basal fertilizer (Huchuand Sithole 1994).

A partial solution for overcoming the excessiverisk that constrains fertilizer use in dry areascan be found in “response farming” techniques(Stewart and Kashasha 1984, Stewart 1991),which use early rainfall events to decide on theamounts of fertilizer to apply. Piha (1993)explored the interaction between nutrient useand rainfall in Zimbabwe. Trials over five yearson farmers’ fields showed that when farmersadjusted fertilizer use to the evolving rainfallpattern in any one season, they obtained 25-42% more yield and 21-41% more profit thanwhen they followed existing fertilizerrecommendations. Piha also showed thatexisting recommendations were too risky forlower rainfall areas and needed to be adjusteddownwards to be profitable.

Such techniques can be refined by using cropsimulation models to predict outcomes undervariable water and N conditions. When thesemodels are used in conjunction with GIS, theresulting information can be used to delineatetarget agroecological areas or groups of farmersfor which a particular input level is appropriate(e.g., Dent and Thornton 1988; Keating, Wafula,

25

and Watiki 1992). Keating, Godwin, and Watiki(1991), using a version of the CERES maizesimulation model modified for Kenya,quantified the economic risks associated withN application for Machakos and Kitui Districts.The risk of economic loss from fertilizerapplication clearly rose as crop availablemoisture declined.

The significance of the recent work by Piha(1993) and similar efforts (Stewart andKashasha 1984, Stewart 1991) is that thejudicious use of inorganic fertilizers can makeproductive and profitable agriculture reliablypossible on the poor soils and in the semiaridconditions that characterize the environmentswhere many of Africa’s smallholders live.

Institutional Change in Researchand Development Organizations

The development and adoption of soilmanagement technologies for smallholdersultimately depends on the capacity of manygroups of people in many countries to interactin new, more productive ways. How willresearch and development organizations needto adapt to ensure that Africa’s soil fertilityproblems are dealt with successfully? Whatshifts in perspective are necessary for researchand extension to accommodate the greatdiversity among smallholders? Whatinstitutional changes are needed to supportproductivity increases in the small-farm sector?In the sections that follow, we propose someanswers to these questions.

Addressing smallholder diversityResearch and development organizations willhave to find better ways of addressing thevariability in the smallholder farmingcommunity. If these organizations are toestablish affordable programs that can addressthe many different problems involved, they

will need to carefully and thoughtfullycharacterize the population into strata ofcoherent and useful size (see Blackie, 1995, foran example of stratification in this context).There are several ways in which knowledge ofthe characteristics of different strata might beexploited to improve the impact of newtechnologies. Two ways are explored here.

Enhanced farm management advice — Thereis no single route to improved maizeproductivity for African farmers. In the“developed” world, farmers have been guidedin the use of new and expensive technologiesby carefully formulated farm managementadvice. Such counsel is rarely available toAfrican farmers. Although the cost of havinghighly qualified farm management advisorsreadily available to all African farmers is clearlyprohibitive, so too are the costs (both social andeconomic) of accepting the continuing declinein African farm productivity. Through jointventures with donors and with private sectorinput suppliers, farm management advice canbe made available to farmers already usinginputs and to farmers whose efficiency can beimproved so as to make input use profitable.

Note that the emphasis in providing betterfarm management advice moves from makinginputs “affordable” (usually by providinginputs in a subsidized form, with all theinherent problems and contradictions ofsubsidies) to making them profitable. Theemphasis also changes from the diagnostic(typified by efforts in farming systems researchand various forms of rapid rural appraisal) andthe prescriptive (ranging from top-downextension efforts to the Training and Visitsystem favored by the World Bank) to aproblem-solving format in which the farmer isactively involved. Such a format will featurerecommendations that are conditional oncircumstances and include “if-and-then”

26

decision making. It provides a framework foreffective research/extension linkages and helpscreate a technology development process that isdriven by smallholders’ needs.

Improving productivity for farmers with thefewest resources — Particular attention needsto be paid to the agricultural productionproblems of the farmers with the fewestresources — typically farmers who do notreliably feed themselves and their families yearon year. This group is analogous to the long-term unemployed who occupy the welfare rollsof the developed world (and remain anintractable problem for those better endowedcountries). It includes the old, the work-shy, thehandicapped, and many single mothers andwidows. Their numbers may be substantial (ashigh as 40% of the smallholder population inMalawi) and are growing. The poverty trapfaced by the poorest families precludes theiractive participation, under presentcircumstances, in a market economy (except asdistress sellers of labor and, sometimes, food).Both equity and reason indicate that theyshould not be ignored — although in fact theyare ignored by the conventional technologydevelopment and extension process.

Cash crops can play an important role inpriming the soil fertility input pump bybringing extra cash income to farmers, butoptions for very poor farmers may be few. InMalawi, for example, burley tobacco may be theonly crop that farmers can grow on their tinyholdings to generate sufficient cash forpurchasing inputs (Carr 1994). But in manysituations it is unrealistic to expect sophisticatedand possibly risky cash cropping to provide thefirst step to a better life for this group offarmers. They are desperately short of cash,

cannot afford the luxury of experimentation,and often lack the confidence and ability todeal unaided with many aspects ofcommercialization. Moreover, cash croppingdepends on reliable, honest markets for inputsand outputs, and targeted production adviceon a new commodity is essential for farmers.

Credit is often proposed as a solution but is ofvalue only to individuals who are periodicallyshort of cash to purchase inputs. Farmers whoare chronically short of cash need alternativesolutions. In some richer African countries, theinformal financial sector (which commonlyincludes such groups as Savings Clubs andRotating Savings and Credit Associations) canbe quite large. Clubs designed and operated bysmallholders meet their special needs forfinancial services. In Malawi, where individualsavings are minute, an innovative effort using acombination of start-up grants and savingsmobilization has been remarkably successful inreaching the poorest farmers around Dowa incentral Malawi (VEZA project). It hasintroduced them to improved maizetechnologies, quickly moving farmers tofinancial viability. Savings rather than credit,therefore, provide the mechanism forintroducing cash-poor smallholders toimproved technologies (Chimedza 1993). Theconventional wisdom holds that mosthouseholds in the smallholder sector have alow marginal propensity to save, and thereforeare not able to invest from savings. Experiencehas shown that the capacity to save is ratherlarger than typically assumed, which gives animportant leverage point when dealing withrural poverty. A sound macroeconomic policythat maintains low monetary inflation isimportant to support such efforts.

27

Institutional change to supportsmallholder productivity increasesThe successful implementation of thetechnology development and transfer processesoutlined in this paper requires the commitmentof substantial resources over extended periods.While the private sector and non-governmentalorganizations (NGOs) will be essential partnersin this effort, high-quality public sector researchand extension will remain a critical element ofthe process (see Blackie, 1994, for a discussionof the role of the private sector). The inadequatefunding base of most public nationalagricultural research systems (NARSs) in Africameans that these institutions face high staffturnover. The scientists who remain often sufferfrom low morale, caused by poor financialincentives as well as the lack of resources forundertaking research. Hence the NARSs, ontheir own, are ill equipped to take on thedifficult task of maintaining institutionalmemory.

The system for developing agriculturaltechnology in Africa is not well adapted tocomprehending and responding to the long-term problems of the continent. Institutionalmemory is limited. Inadequate budgets (andthe poor use of the funds that are available)lead to a collection of short-lived, disparateresearch projects which rarely “follow through”to the farmer. For plant breeding research, theinternational agricultural research system hasbeen able to address these deficiencies to someextent; the results are apparent in the uptake ofimproved germplasm. Structures formaintaining the institutional memory forgermplasm development are comparativelywell developed. The international agriculturalresearch centers (IARCs) have a long, successfulhistory of assisting NARSs in producingimproved varieties by drawing on internationalexperience of varietal development. The IARCsmaintain a comprehensive set of data on

varietal characteristics, on breedingenvironments, and on pest and diseasepressures. A process of collaboration andtraining with national research scientists hasbeen established and is used extensively byplant breeders in developing countries.

By contrast, the effort to maintain a similarcorpus of knowledge on crop management isminuscule. The role of agronomists and socialscientists in the international researchcommunity is more poorly defined than that ofplant breeders. Their numbers and influenceare substantially less. The research vision andagenda for crop management have largely beenleft in the hands of the NARSs, a choicejustified by the belief that crop managementissues are location specific and do not lendthemselves to the kind of broad support thathas proved so useful in crop breeding. Possiblythis belief derives from the initial successes ofthe Green Revolution in Asia, where nationalscientists took up broadly adapted improvedgermplasm and incorporated it into improvedproductivity packages. But in the highlyvariable ecologies and farming communities ofAfrica, ignoring management factors avoidsthe heart of the problem. The continuingunderinvestment in the development of high-quality crop management technology over thelong term has compromised the researchcommunity’s ability to answer the realproblems facing African smallholders. Someeffective ways of organizing an increasedcommitment follow.

Crop management research is typicallyreported in a highly distilled format in theform of farmer recommendations, which sufferfrom two important flaws. The first flaw,which has been mentioned earlier and is welldocumented in the literature, is thatrecommendations rarely take the diversity offarmers’ circumstances into account.

28

The second is that, because of their highlydistilled nature, recommendations are not agood repository for information over the longterm. The data from which therecommendations are derived may be lost longbefore the recommendation itself is discarded.Progress in soil fertility management willrequire information to be retrieved and sharedefficiently among those concerned withpromoting and developing improvedtechnologies. Recent advances in computerdatabases make this task easier. Given thesmall size and limited capacity of many Africanresearch and extension services, obviousopportunities will arise from regionalcollaboration. Some efforts in this directionhave already been made (a recent example isSACCAR, the Southern African Center forCooperation in Agricultural Research andTraining) but have failed to realize theirpotential.

The needed impacts from soil fertility workwill be obtained through a long-termcommitment to research and extension byinterdisciplinary, interinstitutional, andintercountry groups of staff that include notonly technical scientists but also socialscientists, extensionists, the private sector, andNGO staff. Opportunities need to be created forthese people to work more closely on commontopics and trials. A climate of mutual reviewand constructive criticism is essential. Financialconstraints mean no single country orinstitution can bring sufficient resources to bearon these widespread, complex issues. There is aclear need for continuity in resources focusedon soil fertility improvement, efficiencies fromregional cooperation in the use of thoseresources, and better regional access to results.One way of developing a more integratedapproach is through formal networks.

A variety of networks related to soil fertilityresearch are working at several levels. Themost important process-orientated soil fertilityresearch network in Africa is AfNet, run by theTSBF Program. AfNet brings together Africanscientists to work on improving thesynchronization of soil nutrient supply tonutrient demand by the crop, through sitecharacterization and the use of commonmethods (e.g., Seward 1995). A good exampleof a more applied soil fertility research andextension network is the network established inlate 1994 by the Rockefeller Foundation withthe Malawian and Zimbabwean nationalresearch and extension programs andCIMMYT. This network emphasizes jointresearch priority setting, planning, andintegration through meetings and peer review;research on high-priority issues, includingnetwork trials across maize-basedagroecologies; information exchange andtraining for network scientists; and thedistribution and use of research results andother information through enhancedinteraction between the farmer, extension, andresearch (Waddington 1995).

These networks overcome some of the negativeattributes of previous networking efforts; theyare internally driven by the participatingscientists rather than externally driven bydonors. But this is not a sufficient condition forsuccess in addressing client needs. We need tomove even further to networks that take thelead on integrating farmers, NGOs, extensionservices, and policy makers with research inthe testing and dissemination of appropriatesoil fertility technology. Without this kind ofconcerted action, many countries in sub-Saharan Africa will suffer from a weakeningnatural resource base and a continuing declinein the standard of living, especially amongpeople who depend on agriculture.

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